Black Spots on Tomato Leaves May Be Septoria

Q. I have these small black spots developing all over my tomato leaves. Any idea what is wrong with my tomato plant? 

Possible Septoria leaf spot disease on new transplants

A. From your pictures it looks like you could have a couple of things going on. The tiny black or brown spots on the leaves may be a disease called Septoria leaf spot. As a precaution, I would apply a fungicide for vegetables immediately and follow the label directions to a tee.

Any general fungicide for vegetables will work. It usually requires several applications in sequence. Push some new growth with a light application of a tomato fertilizer.

Another shot of possible Septoria.

Fungicides are primarily meant for disease prevention, not for curing a disease once the plant has it. Applying a fungicide protects new growth as it emerges so new growth should be healthy while the infected growth does not get worse.

The other option is to pull it out and start over.

Secondly, never apply irrigation water with a sprinkler; use drip irrigation.

If you bought these plants from a local store it probably came with the plant when it was grown in the greenhouse and shipped to the store. This disease is fairly easy to control if a greenhouse is kept clean and the plants kept healthy.

Such is the problem when buying low-priced transplants. They were most likely infected when you bought them. There were probably some leaves already showing these spots.

Your other pictures show leaves of tomato with edges that are scorching. These scorched margins have a yellow inner margin. This is possible salt damage.

Reminds me more of salt damage but ......

Soak the soil with water. Use a soil wetting agent like EZ Wet or comparable and apply it to the soil to remove salts. Hopefully you amended your soil with compost at the time of planting and you used a pre plant fertilizer.

Also some leaves showed signs of yellowing which may be due to lack of fertilizer applied at the time of planting. Once tomatoes start setting fruit it is important to feed them lightly to continue healthy growth.

Take a look at these fact sheets and pics.

Cornell's Fact Sheet on Septoria on Tomato

Missouri Botanical Garden Fact Sheet on Septoria on Tomato